Methods of controlling hydroformylation processes

ABSTRACT

The present invention relates to methods of controlling hydroformylation processes for producing normal (N) and iso (I) aldehydes at a N:I ratio. In one aspect, a method of controlling a hydroformylation process comprises contacting an olefin with carbon monoxide, hydrogen and a catalyst, the catalyst comprising (A) a transition metal, (B) a monophosphine, and (C) a tetraphosphine having the structure described herein, the contacting conducted in one or more reaction zones and at hydroformylation conditions to produce a blend of normal (N) and iso (I) aldehydes at a N:I ratio, the method comprising at least one of increasing the N:I ratio by adding additional tetraphosphine to a reaction zone; decreasing the N:I ratio by adding additional monophosphine to a reaction zone; or increasing the N:I ratio by volatilization of the free monophosphine.

FIELD

The present invention relates to methods of controlling hydroformylation processes for producing normal (N) and iso (I) aldehydes at a N:I ratio.

BACKGROUND

It is known in the art that aldehydes may be readily produced by reacting an olefinically unsaturated compound with carbon monoxide and hydrogen in the presence of a solubilized rhodium-triorganophosphorous ligand complex catalyst and that a preferred type of such processes involves continuous hydroformylation. For example, U.S. Pat. No. 3,527,809 discloses the hydroformylation of alpha-olefins to produce aldehydes at low temperatures and pressures. The process employs certain rhodium complexes to effectively catalyze, under a defined set of variables in the presence of select triorganophosphorous ligands, the hydroformylation of olefins with hydrogen and carbon monoxide.

Among the catalysts described in U.S. Pat. No. 3,527,809 are compounds containing rhodium and triarylphosphorous ligands, in particular triarylphosphine ligands exemplified by triphenylphosphine (“TPP”). Commercial hydroformylation processes have successfully employed the rhodium-TPP catalyst for decades, and a key aspect of operation is the use of a large excess of TPP relative to rhodium. For example, industrial propylene hydroformylation processes often operate with TPP concentrations of 10-12 weight percent based on the total mass of the reaction fluid. Such high concentrations of TPP are used to achieve the desired product regioselectivity and to enhance catalyst stability.

For hydroformylation processes, product regioselectivity is typically expressed as the ratio of linear (or normal) product to branched (or iso) aldehyde product. As used herein, this ratio of linear (or normal) product to branched (or iso) aldehyde product will be referred to as the “N:I ratio” or “N:I”. Although rhodium-TPP catalysis is effective technology, it is difficult to increase the N:I to values greater than about 10:1. While the branched product has value, the linear product is often preferred. Selectivity to linear products could be increased by using a different catalyst promoter, for example, particular chelating organopolyphosphorous ligands (e.g., certain bisphosphites) are known to demonstrate an N:I in excess of 10:1, but such changes in an industrial setting would involve dumping the existing catalyst, recovering the rhodium via precious metal recovery (“PMR”), possible equipment changes, etc. The loss of production, PMR costs, and purchasing of process equipment associated with such an effort could be quite expensive.

It would be desirable to have a facile, cost-effective method to control the N:I ratio over a broad range.

SUMMARY

The present invention relates to methods of controlling a hydroformylation process for producing normal (N) and iso (I) aldehydes at a N:I ratio that provides a number of advantages in various embodiments. For example, according to some embodiments, it has surprisingly been discovered that a catalyst comprised of a transition metal, monophosphine, and a tetraphosphine can be used to provide an N:I ratio over a broad range (e.g., from 3:1 to greater than 35:1 in various embodiments). Moreover, both the rate of catalyst deactivation and the amount of tetraphosphine consumed per unit time (ligand usage) are quite low in some embodiments.

In one aspect, a method of controlling a hydroformylation process for producing normal (N) and iso (I) aldehydes, the process comprising contacting an olefin with carbon monoxide, hydrogen and a catalyst, the catalyst comprising (A) a transition metal, (B) a monophosphine, and (C) a tetraphosphine having the following structure:

wherein each P is a phosphorous atom, and each of R¹-R⁴⁶ are independently hydrogen, a C1 to C8 alkyl group, an aryl group, an alkaryl group, or a halogen, the contacting conducted in one or more reaction zones and at hydroformylation conditions to produce a blend of normal (N) and iso (I) aldehydes at a N:I ratio, comprises at least one of:

-   -   (1) increasing the N:I ratio by adding additional tetraphosphine         to a reaction zone;     -   (2) decreasing the N:I ratio by adding additional monophosphine         to a reaction zone; or     -   (3) increasing the N:I ratio by volatilization of the free         monophosphine.

These and other embodiments are discussed in more detail in the Detailed Description below.

DETAILED DESCRIPTION

All references to the Periodic Table of the Elements and the various groups therein are to the version published in the CRC Handbook of Chemistry and Physics, 72nd Ed. (1991-1992) CRC Press, at page I-11.

Unless stated to the contrary, or implicit from the context, all parts and percentages are based on weight and all test methods are current as of the filing date of this application. For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety (or its equivalent US version is so incorporated by reference) especially with respect to the disclosure of definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure) and general knowledge in the art.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably. The terms “comprises,” “includes,” and variations thereof do not have a limiting meaning where these terms appear in the description and claims.

Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed in that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). For the purposes of the invention, it is to be understood, consistent with what one of ordinary skill in the art would understand, that a numerical range is intended to include and support all possible sub-ranges that are included in that range. For example, the range from 1 to 100 is intended to convey from 1.01 to 100, from 1 to 99.99, from 1.01 to 99.99, from 40 to 60, from 1 to 55, etc. Also herein, the recitations of numerical ranges and/or numerical values, including such recitations in the claims, can be read to include the term “about.” In such instances the term “about” refers to numerical ranges and/or numerical values that are substantially the same as those recited herein.

As used herein, the term “ppmw” means parts per million by weight.

For purposes of this invention, the term “hydrocarbon” is contemplated to include all permissible compounds having at least one hydrogen and one carbon atom. Such permissible compounds may also have one or more heteroatoms. In a broad aspect, the permissible hydrocarbons include acyclic (with or without heteroatoms) and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic organic compounds that can be substituted or unsubstituted.

As used herein, the term “substituted” is contemplated to include all permissible substituents of organic compounds unless otherwise indicated. In a broad aspect, the permissible substituents include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic substituents of organic compounds. Illustrative substituents include, for example, alkyl, alkyloxy, aryl, aryloxy, hydroxyalkyl, aminoalkyl, in which the number of carbons can range from 1 to 20 or more, preferably from 1 to 12, as well as hydroxy, halo, and amino. The permissible substituents can be one or more and the same or different for appropriate organic compounds. This invention is not intended to be limited in any manner by the permissible substituents of organic compounds.

As used herein, the term “hydroformylation” is contemplated to include, but is not limited to, all hydroformylation processes that involve converting one or more substituted or unsubstituted olefinic compounds or a reaction mixture comprising one or more substituted or unsubstituted olefinic compounds to one or more substituted or unsubstituted aldehydes or a reaction mixture comprising one or more substituted or unsubstituted aldehydes. The aldehydes may be asymmetric or non-asymmetric.

The terms “reaction fluid,” “reaction medium” and “catalyst solution” are used interchangeably herein, and may include, but are not limited to, a mixture comprising: (a) a transition metal-monophosphine complex catalyst (e.g., a rhodium-triphenylphosphine complex catalyst), (b) a transition metal-tetraphosphine complex catalyst (e.g., a rhodium-tetraphosphine complex catalyst), (c) free monophosphine (e.g., triphenylphospine), (d) free tetraphosphine, (e) aldehyde products formed in the reaction, (f) unreacted reactants, (g) a solvent for said transition metal complex catalysts and said free phosphine ligands, and, optionally (h) monophosphine ligand and tetraphosphine ligand degradation products. The reaction fluid can encompass, but is not limited to, (a) a fluid in a reaction zone, (b) a fluid stream on its way to a separation zone, (c) a fluid in a separation zone, (d) a recycle stream, (e) a fluid withdrawn from a reaction zone or separation zone, (f) a fluid in an external cooler, and (g) ligand degradation products.

The term “ligand degradation products” is contemplated to include, but is not limited to any and all compounds resulting from one or more chemical transformations of at least one of the tetraphosphine and or monophosphine molecules charged to the reaction fluid. Such compounds may include but are not limited to triphosphine or diphosphine compounds derived from rhodium-promoted cleavage of the parent tetraphosphine as well as the smaller phosphine moieties resulting from said cleavage side reactions. Ligand degradation products are also contemplated to include alkyldiarylphosphines which are known to be present in rhodium-triarylphosphine hydroformylation catalyst solutions (see, for example, U.S. Pat. No. 4,297,239, col. 5). Ligand degradation products are additionally contemplated to include any and all compounds which result from oxidation of phosphine moieties. For example, ligand degradation products may comprise phosphine oxides derived from monophosphine introduced to the process, from partial or complete oxidation of tetraphosphine introduced to the process, or from the oxidation of phosphine compounds resulting from rhodium-promoted side reactions (e.g. oxidation of triphosphine compounds derived from the parent tetraphosphine).

As used herein the terms “tetradentate phosphine” and “tetraphosphine” are used interchangeably and are contemplated to comprise compounds containing four phosphine atoms each one of which is bound to three carbon atoms.

As used herein the terms “monodentate phosphine” and “monophosphine” are used interchangeably and comprise compounds which contain a single phosphine atom bound to three carbon atoms.

As used herein the terms “rhodium complex”, “rhodium complex catalyst”, and “catalyst complex” are used interchangeably and are contemplated to comprise at least one rhodium atom with ligands bound or coordinated via electron interaction. Examples of such ligands include but are not limited to monophosphine, tetradentate phosphine, carbon monoxide, propylene and hydrogen.

As used herein, the term “free” phosphine is contemplated to comprise monophosphine or tetraphosphine molecules that are not bound or coordinated to rhodium.

In general, the present invention is directed to methods for controlling the N:I ratio of aldehydes produced by a hydroformylation process. The catalyst composition includes two ligands, a monophosphine and a tetraphosphine, and the N:I ratio of the aldehydes produced can be increased or decreased by adding one ligand or other to a reaction zone. Some embodiments of the methods facilitate the production of aldehydes over a surprisingly broad range of N:I ratios without the disadvantages often associated with changing the ligand utilized in a catalyst composition.

In one aspect, a method of controlling a hydroformylation process for producing normal (N) and iso (I) aldehydes, the process comprising contacting an olefin with carbon monoxide, hydrogen and a catalyst, the catalyst comprising (A) a transition metal, (B) a monophosphine, and (C) a tetraphosphine having the following structure:

wherein each P is a phosphorous atom, and each of R¹-R⁴⁶ are independently hydrogen, a C1 to C8 alkyl group, an aryl group, an alkaryl group, or a halogen, the contacting conducted in one or more reaction zones and at hydroformylation conditions to produce a blend of normal (N) and iso (I) aldehydes at a N:I ratio, comprises at least one of:

-   -   (1) increasing the N:I ratio by adding additional tetraphosphine         to a reaction zone;     -   (2) decreasing the N:I ratio by adding additional monophosphine         to a reaction zone; or     -   (3) increasing the N:I ratio by volatilization of the free         monophosphine.         In some embodiments, the transition metal comprises rhodium. In         some embodiments, the olefin is propylene.

The monophosphine, in some embodiments, is one or more of the following: triphenylphosphine, tris(o-tolyl)phosphine, trinaphthylphosphine, tri(p-methoxyphenyl) phosphine, tri(m-chlorophenyl)-phosphine, tribenzylphosphine, tricyclohexylphosphine, dicyclohexylphenylphosphine, cyclohexyldiphenylphosphine, and trioctylphosphine. The monophosphine is triphenylphosphine in some embodiments. In some embodiments, the catalyst comprises a mixture of different species of monophosphines.

In some embodiments, each of R¹-R⁴⁶ in the structure for the tetraphosphine are hydrogen. In some embodiments the catalyst comprises one or more of the following tetraphosphines:

In some embodiments, the transition metal comprises rhodium, the monophosphine is triphenylphospine, each of R¹-R⁴⁶ are hydrogen, and the olefin comprises propylene.

In some embodiments, the amount of monophosphine in the reaction zone is greater than 1.5 weight percent based on the total weight of reaction fluid in the reaction zone. The amount of monophosphine in the reaction zone, in some embodiments, is from 1.5 to 13 weight percent based on the total weight of reaction fluid in the reaction zone. In some embodiments, the amount of tetraphosphine in the reaction zone is greater than 0.06 weight percent based on the total weight of reaction fluid in the reaction zone. The amount of tetraphosphine in the reaction zone, in some embodiments, is from 0.1 to 9 weight percent based on the total weight of reaction fluid in the reaction zone. In some embodiments, the amount of monophosphine in the reaction zone is greater than 1.5 weight percent and the amount of tetraphosphine in the reaction zone is greater than 0.06 weight percent, each based on the total weight of reaction fluid in the reaction zone. In some embodiments, the amount of monophosphine in the reaction zone is from 1.5 to 13 weight percent and the amount of tetraphosphine in the reaction zone is from 0.1 to 9 weight percent, each based on the total weight of reaction fluid in the reaction zone.

Hydrogen and carbon monoxide may be obtained from any suitable source, including petroleum cracking and refinery operations.

Syngas (from synthesis gas) is the name given to a gas mixture that contains varying amounts of CO and H₂. Production methods are well known. Hydrogen and CO typically are the main components of syngas, but syngas may contain CO₂ and inert gases such as N₂ and Ar. The molar ratio of H₂ to CO varies greatly but generally ranges from 1:100 to 100:1 and preferably between 1:10 and 10:1. Syngas is commercially available and is often used as a fuel source or as an intermediate for the production of other chemicals. The most preferred H₂:CO molar ratio for chemical production is between 3:1 and 1:3 and usually is targeted to be between about 1:2 and 2:1 for most hydroformylation applications. Syngas mixtures are a preferred source of hydrogen and CO.

The olefinic starting material reactants that may be employed in the hydroformylation reactions encompassed by of this invention can be terminally or internally unsaturated and be of straight-chain, branched-chain or cyclic structure. Such olefins can contain from 2 to 20 carbon atoms and may contain one or more ethylenic unsaturated groups. Moreover, such olefins may contain groups or substituents which do not essentially adversely interfere with the hydroformylation process such as carbonyl, carbonyloxy, oxy, hydroxy, oxycarbonyl, halogen, alkoxy, aryl, alkyl, haloalkyl, and the like. Illustrative olefinic unsaturated compounds include alpha olefins, internal olefins, alkyl alkanoates, alkenyl alkanoates, alkenyl alkyl ethers, alkenols, and the like, e.g. ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1,-dodecene, 1-octadecene, 2-butene, isobutylene, 2-methylbutene, 2-hexene, 3-hexene, 2-heptene, cyclohexene, propylene dimers, propylene trimers, propylene tetramers, butene dimers, butene trimers, 2-ethyl-1-hexene, styrene, 3-phenyl-1-propene, 1,4-hexadiene, 1,7-octadiene, 3-cyclohexyl-1-butene, and the like. Of course, it is understood that mixtures of different olefinic starting materials can be employed, if desired. Embodiments of the present invention can be particularly useful in the hydroformylation of C₃ and higher olefins. Thus, in some embodiments, the olefinic unsaturated starting materials are alpha olefins containing from 3 to 20 carbon atoms, and internal olefins containing from 3 to 20 carbon atoms as well as starting material mixtures of such alpha olefins and internal olefins.

A solvent advantageously is employed in the hydroformylation process. Any suitable solvent that does not unduly interfere with the hydroformylation process can be used. By way of illustration, suitable solvents for rhodium catalyzed hydroformylation processes include those disclosed, for example, in U.S. Pat. Nos. 3,527,809; 4,148,830; 5,312,996; and 5,929,289. Non-limiting examples of suitable solvents include saturated hydrocarbons (alkanes), aromatic hydrocarbons, ethers, aldehydes, ketones, nitriles, alcohols, esters, and aldehyde condensation products. Specific examples of solvents include: tetraglyme, pentanes, cyclohexane, heptanes, benzene, xylene, toluene, diethyl ether, tetrahydrofuran, butyraldehyde, and benzonitrile. The organic solvent may also contain dissolved water up to the saturation limit. Illustrative preferred solvents include ketones (e.g. acetone and methylethyl ketone), esters (e.g. ethyl acetate, di-2-ethylhexyl phthalate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), hydrocarbons (e.g. toluene), nitrohydrocarbons (e.g., nitrobenzene), ethers (e.g., tetrahydrofuran (THF)) and sulfolane. In rhodium catalyzed hydroformylation processes, it may be preferred to employ, as a primary solvent, aldehyde compounds corresponding to the aldehyde products desired to be produced and/or higher boiling aldehyde liquid condensation by-products, for example, as might be produced in situ during the hydroformylation process, as described for example in U.S. Pat. Nos. 4,148,830 and 4,247,486. The primary solvent will normally eventually comprise both aldehyde products and higher boiling aldehyde liquid condensation by-products (“heavies”), due to the nature of the continuous process. The amount of solvent is not especially critical and need only be sufficient to provide the reaction medium with the desired amount of transition metal concentration. Typically, the amount of solvent ranges from about 5 percent to about 95 percent by weight, based on the total weight of the reaction fluid. Mixtures of solvents may be employed.

The catalyst of this invention comprises a transition metal, monophosphine, and a tetraphosphine. In certain particularly useful embodiments, the catalyst comprises rhodium a monophosphine, and a tetraphosphine. The most desirable catalyst is free of metal-bound halogens such as chlorine, and contains hydrogen, carbon monoxide and at least one of the monophosphine and tetraphosphine complexed with rhodium metal to produce a catalyst soluble in the aforementioned liquid phase and stable under the conditions of the reaction.

The transition metal can include Group 8, 9 and 10 metals selected from rhodium (Rh), cobalt (Co), iridium (Ir), ruthenium (Ru), iron (Fe), nickel (Ni), palladium (Pd), platinum (Pt), osmium (Os) and mixtures thereof, with preferred metals being rhodium, cobalt, iridium and ruthenium, more preferably rhodium, cobalt and ruthenium, especially rhodium.

The number of available coordination sites on such metals is well known in the art. Thus the catalytic species, which may comprise a complex catalyst mixture, may comprise monomeric, dimeric or higher nuclearity forms, which are preferably characterized by at least one organophosphine-containing molecule complexed per one molecule of metal, e.g., rhodium. For instance, it is considered that the catalytic species of the preferred catalyst employed in a hydroformylation reaction may be complexed with carbon monoxide and hydrogen in addition to the organophosphine ligands in view of the carbon monoxide and hydrogen gas employed by the hydroformylation reaction.

In certain preferred embodiments, the transition metal is rhodium. Rhodium can be introduced into the liquid phase as a preformed catalyst, e.g., a stable crystalline solid, rhodium hydridocarbonyl-tris(triphenyl phosphine), RhH(CO) (PPh₃)₃. The rhodium can be introduced to the liquid body as a precursor form which is converted in situ into the catalyst. Examples of such precursor form are rhodium carbonyl triphenylphosphine acetylacetonate, Rh₂O₃, Rh₄(CO)₁₂, Rh₆(CO)₁₆, and rhodium dicarbonyl acetylacetonate. Both the catalyst compounds which will provide active species in the reaction medium and their preparation are known by the art, see Brown et al., Journal of the Chemical Society, 1970, pp. 2753-2764.

In general the optimum catalyst concentration depends on the concentration of the alpha-olefin, such as propylene. For example, the higher the propylene concentration the lower usually will be the catalyst concentration needed to achieve a given conversion rate to aldehyde products in a given size of reactor. Recognizing that partial pressures and concentration are related, the use of higher propylene partial pressure leads to an increased proportion of propylene in the “off gas” from the liquid body. Since it may be necessary to purge part of the gas stream from the product recovery zone before recycle to the liquid body in order to remove a portion of the propane which may be present, the higher the propylene content of the “off gas” is, the more propylene that will be lost in the propane purge stream. Thus it is necessary to balance the economic value of the propylene lost in the propane purge stream against the capital savings associated with lower catalyst concentration.

The rhodium complex catalysts may be in homogeneous or heterogeneous form. For instance, preformed rhodium hydrido-carbonyl-phosphine ligand catalysts may be prepared and introduced into a hydroformylation reaction mixture. More preferably, the rhodium-phosphine ligand complex catalysts can be derived from a rhodium catalyst precursor that may be introduced into the reaction medium for in situ formation of the active catalyst. For example, rhodium catalyst precursors such as rhodium dicarbonyl acetylacetonate, Rh₂O₃, Rh₄(CO)₁₂, Rh₆(CO)₁₆, Rh(NO₃)₃ and the like may be introduced into the reaction mixture along with the monophosphine and or tetraphosphine for the in situ formation of the active catalyst. In a preferred embodiment, rhodium dicarbonyl acetylacetonate is employed as a rhodium precursor and combined with at least one of the monophosphine and tetraphosphine in a solvent and introduced into the reactor along with syn gas for the in situ formation of the active catalyst. Additional monophosphine and or tetraphosphine may be added as necessary to achieve and maintain the desired concentrations. In any event, it is sufficient that carbon monoxide, hydrogen, monophosphine and tetraphosphine are all ligands that are capable of being complexed with the metal and that an active metal-ligand catalyst is present in the reaction mixture under the conditions used in the hydroformylation reaction.

In some embodiments, a catalyst composition is formed in a mix tank by combining the rhodium catalyst precursor with monophosphine and/or tetraphosphine. If the rhodium catalyst precursor is only combined with one of the two ligands prior to addition to the reactor, the other ligand can be added separately to the reactor to form the catalyst composition in the reactor.

The amount of rhodium complex catalyst present in the reaction fluid need only be that minimum amount necessary to produce the desired production rate. In general, rhodium concentrations in the range of from 150 ppmw to 1200 ppmw, calculated as free metal in the reaction fluid in a hydroformylation reactor, should be sufficient for most processes, while it is generally preferred to employ from 150 to 800 ppmw of metal, and more preferably from 150 to 500 ppmw of rhodium.

The amount of monophosphine in the catalyst composition (whether formed entirely in a mix tank or formed in the reactor) is at least 40 moles of monophosphine per mole of transition metal (rhodium). In some embodiments, the amount of monophosphine in the catalyst composition (whether formed entirely in a mix tank or formed in the reactor) is from 40 to 350 moles of monophosphine per mole of transition metal (rhodium). The amount of tetraphosphine in the catalyst composition (whether formed entirely in a mix tank or formed in the reactor) is at least 1 mole of tetraphosphine per mole of transition metal (rhodium). In some embodiments, the amount of tetraphosphine in the catalyst composition (whether formed entirely in a mix tank or formed in the reactor) is from 1 to 10 moles of tetraphosphine per mole of transition metal (rhodium). The amount of moles of monophosphine or tetraphosphine is measured by high performance liquid chromatography (HPLC) as described in the Examples. The amount of moles of rhodium is measured by atomic absorption.

While tetraphosphine ligand can conceivably degrade to one or more monophosphine compounds, the amount of monophosphine in the catalyst compositions and the reaction fluid according to embodiments of the present invention are much greater than would be expected to potentially appear through degradation. In other words, the vast majority of the monophosphine in the catalyst composition or reaction fluid is added or charged to the catalyst composition or reaction fluid to provide the specified amount (e.g., not derived from the tetraphosphine present in the catalyst composition or reaction fluid).

For commercial operations, ligand concentrations must be maintained by periodic or continuous additions. To do so, the concentrations of ligands in the reaction fluid are routinely measured by one or more analytical techniques; high performance liquid chromatography (HPLC) is typically preferred. Unless otherwise indicated herein, when referring to the amount of ligand in a reaction, the ligand concentration is determined by HPLC as described in the Examples. Ligand concentrations in such analyses are often reported as weight percent; thus it is often convenient to use these units for continuous operation. In some embodiments, the amount of monophosphine in the reaction fluid in a reactor of a hydroformylation process is greater than or equal to 1.5 weight percent based on the total weight of the reaction fluid in the reactor. In some embodiments, the amount of monophosphine in the reaction fluid in a reactor of a hydroformylation process is from 1.5 to 13 weight percent based on the total weight of the reaction fluid in the reactor. In some embodiments, the amount of tetraphosphine in the reaction fluid in a reactor of a hydroformylation process is greater than or equal to 0.06 weight percent based on the total weight of the reaction fluid in the reactor. In some embodiments, the amount of tetraphosphine in the reaction fluid in a reactor of a hydroformylation process is from 0.1 to 9 weight percent based on the total weight of the reaction fluid in the reactor. In some embodiments wherein R¹-R⁴⁶ in the tetraphosphine shown above are each hydrogen, the amount of tetraphosphine in the reaction fluid in a reactor of a hydroformylation process is from 0.1 to 4 weight percent based on the total weight of the reaction fluid in the reactor.

By way of illustration, a preferred catalyst precursor composition consists essentially of a solubilized rhodium complex precursor, at least one of the monophosphine and tetraphosphine, and a solvent. The monophosphine and or the tetraphosphine will readily replace one of the carbonyl ligands of the rhodium acetylacetonate complex precursor as witnessed by the evolution of carbon monoxide gas. Upon introduction of the catalyst precursor composition to the reactor, additional monophosphine or tetraphosphine may optionally then be added to achieve the target concentrations within the reaction fluid.

Accordingly, the rhodium-ligand complex catalysts in the reaction fluid of a hydroformylation reactor advantageously comprise rhodium complexed with carbon monoxide and at least one of monophosphine and tetraphosphine. In one embodiment, mixtures of rhodium-ligand complexes are employed. For example, the catalyst additionally comprises rhodium complexed with carbon monoxide and tetradentate phosphine in a chelated and/or non-chelated fashion. The catalyst additionally comprises rhodium complexed with one or more monophosphine molecules and carbon monoxide.

In addition to the rhodium complex catalyst, free monophosphine (i.e., monophosphine that is not complexed with the metal) will also be present in the reaction fluid, and may also be present in a catalyst composition prior to being provided to a reactor depending on the particular composition. The significance of free ligand is taught in U.S. Pat. No. 3,527,809, GB 1,338,225, and Brown et al., supra., pages 2759 and 2761. In some embodiments, the hydroformylation process of this invention may involve from 1 weight percent or higher of free monophosphine in the reaction medium. The reaction fluid may also contain free tetradentate phosphine. In some such embodiments, the concentration of free tetradentate phosphine may range from 0.1 to 10 moles per mole of rhodium.

The monophosphine compounds that may serve as ligands in embodiments of the present invention are compounds of Formula I:

wherein P is a phosphorous atom, and each of Y¹-Y³ are independently an aryl group, an alkaryl group, a cycloalkyl group, a benzyl group, a C3 to C8 alkyl group, an alkoxyl group of 1-8 carbons, an aryloxy group, or a halogen. Illustrative examples include but are not limited to triphenylphosphine, tris(o-tolyl)phosphine, trinaphthylphosphine, tri(p-methoxyphenyl) phosphine, tri(m-chlorophenyl)-phosphine, tribenzylphosphine, tricyclohexylphosphine, dicyclohexylphenylphosphine, cyclohexyldiphenylphosphine, trioctylphosphine, and the like. In some embodiments, the monophosphine compounds can be sterically hindered phosphines such as those described in U.S. Pat. Nos. 4,283,562 and 5,741,945. For example, in some such embodiments, Y¹-Y³ in Formula I can independently be a substituted or unsubstituted C3 to C8 alkyl, a substituted or unsubstituted C5 to C8 cycloalkyl group, or a substituted or unsubstituted C6 to C12 aryl group.

Mixtures of monophosphines can be used in some embodiments.

The tetraphosphine compounds that may serve as the ligands in embodiments of the present invention are compounds of Formula II:

wherein each P is a phosphorous atom, and each of R¹-R⁴⁶ are independently hydrogen, a C1 to C8 alkyl group, an aryl group, an alkaryl group, a haloalkyl group, or a halogen. In a preferred embodiment, each of R¹-R⁴⁶ is hydrogen. Other examples of tetraphosphines that can be used in some embodiments are described elsewhere in the present specification.

Mixtures of tetraphosphines can be used in some embodiments.

Hydroformylation processes, and conditions for their operation, are well known. In a typical embodiment, an olefin (e.g., propylene) is hydroformylated in a continuous or semi-continuous fashion, with the product being separated in a separation zone, and the concentrated catalyst solution being recycled back into one or more reactors. The recycle procedure generally involves withdrawing a portion of the liquid reaction medium containing the catalyst and aldehyde product from the hydroformylation reactor, i.e., reaction zone, either continuously or intermittently, and recovering the aldehyde product therefrom by use of a composite membrane, such as disclosed in U.S. Pat. Nos. 5,430,194 and 5,681,473, or by the more conventional and preferred method of distilling it, i.e. vaporization separation, in one or more stages under normal, reduced or elevated pressure, as appropriate, in a separate distillation zone, the non-volatilized metal catalyst containing residue being recycled to the reaction zone as disclosed, for example, in U.S. Pat. No. 5,288,918. Condensation of the volatilized materials, and separation and further recovery thereof, e.g., by further distillation, can be carried out in any conventional manner, the crude aldehyde product can be passed on for further purification and isomer separation, if desired, and any recovered reactants, e.g., olefinic starting material and syngas, can be recycled in any desired manner to the hydroformylation zone (reactor). The recovered metal catalyst containing retentate of such membrane separation or recovered non-volatilized metal catalyst containing residue of such vaporization separation can be recycled, to the hydroformylation zone (reactor) in any conventional manner desired.

In a preferred embodiment, the hydroformylation reaction fluid contains at least some amount of six main ingredients or components, i.e., the aldehyde product, a rhodium-triphenylphosphine ligand complex catalyst, free triphenylphosphine ligand, a rhodium-tetraphosphine ligand complex catalyst, free tetraphosphine ligand, and a solvent for said catalysts and said free ligands. The hydroformylation reaction mixture compositions can and normally will contain additional ingredients such as those that have either been deliberately employed in the hydroformylation process or formed in situ during said process. Examples of such additional ingredients include unreacted olefin starting material, carbon monoxide and hydrogen gases, and in situ formed by-products, ligand degradation compounds, and high boiling liquid aldehyde condensation by-products, as well as other inert co-solvent type materials or hydrocarbon additives, if employed.

The hydroformylation reaction conditions employed may vary. For instance, the total gas pressure of hydrogen, carbon monoxide and olefin starting compound of the hydroformylation process may range from 1 to 69,000 kPa. In general, however, it is preferred that the process be operated at a total gas pressure of hydrogen, carbon monoxide and olefin starting compound of less than 14,000 kPa and more preferably less than 3,400 kPa. The minimum total pressure is limited predominantly by the amount of reactants necessary to obtain a desired rate of reaction. More specifically, the carbon monoxide partial pressure of the hydroformylation process is preferably from 1 to 6,900 kPa, and more preferably from 21 to 5,500 kPa, while the hydrogen partial pressure is preferably from 34 to 3,400 kPa and more preferably from 69 to 2,100 kPa. In general, the molar ratio of gaseous H₂:CO may range from 1:10 to 100:1 or higher, the more preferred molar ratio being from 1:10 to 10:1.

In general, the hydroformylation process may be conducted at any operable reaction temperature. Advantageously, the hydroformylation process is conducted at a reaction temperature from −25° C. to 200° C., preferably from 50° C. to 120° C.

The hydroformylation process may be carried out using one or more suitable reactors such as, for example, a continuous stirred tank reactor (CSTR), venturi reactor, bubble column reactor, or a slurry reactor. The optimum size and shape of the reactor will depend on the type of reactor used. The reaction zone employed may be a single vessel or may comprise two or more discrete vessels. The separation zone employed may be a single vessel or may comprise two or more discrete vessels. The reaction zone(s) and separation zone(s) employed herein may exist in the same vessel or in different vessels. For example, reactive separation techniques such as reactive distillation, and reactive membrane separation may occur in the reaction zone(s).

The hydroformylation process can be conducted with recycle of unconsumed starting materials if desired. The reaction can be conducted in a single reaction zone or in a plurality of reaction zones, and in series or in parallel. The reaction steps may be effected by the incremental addition of one of the starting materials to the other. Also, the reaction steps can be combined by the joint addition of the starting materials. The starting materials may be added to each or all of the reaction zones in series. When complete conversion is not desired or not obtainable, the starting materials can be separated from the product, for example by distillation, and the starting materials then recycled back into the reaction zone.

The hydroformylation process may be conducted in either glass lined, stainless steel or similar type reaction equipment. The reaction zone may be fitted with one or more internal and/or external heat exchanger(s) in order to control undue temperature fluctuations, or to prevent any possible “runaway” reaction temperatures.

The hydroformylation process of this invention may be conducted in one or more steps or stages. The exact number of reaction steps or stages will be governed by the best compromise between capital costs and achieving high catalyst selectivity, activity, lifetime and ease of operability, as well as the intrinsic reactivity of the starting materials in question and the stability of the starting materials and the desired reaction product to the reaction conditions.

In one embodiment, the hydroformylation process useful in this invention may be carried out in a multistaged reactor such as described, for example, in U.S. Pat. No. 5,728,893. Such multistaged reactors can be designed with internal, physical barriers that create more than one theoretical reactive stage per vessel.

It is generally preferred to carry out the hydroformylation process in a continuous manner. Continuous hydroformylation processes are well known in the art. The continuous process can be carried out in a single pass mode, i.e., wherein a vaporous mixture comprising unreacted olefinic starting material(s) and vaporized aldehyde product is removed from the liquid reaction mixture from whence the aldehyde product is recovered and make-up olefinic starting material(s), carbon monoxide and hydrogen are supplied to the liquid reaction medium for the next single pass through without recycling the unreacted olefinic starting material(s). Such types of recycle procedure are well known in the art and may involve the liquid recycling of the metal-organophosphorous complex catalyst fluid separated from the desired aldehyde reaction product(s), such as disclosed, for example, in U.S. Pat. No. 4,148,830 or a gas recycle procedure such as disclosed, for example, in U.S. Pat. No. 4,247,486, as well as a combination of both a liquid and gas recycle procedure if desired. The most preferred hydroformylation process comprises a continuous liquid catalyst recycle process. Suitable liquid catalyst recycle procedures are disclosed, for example, in U.S. Pat. Nos. 4,668,651; 4,774,361; 5,102,505 and 5,110,990.

In one embodiment, the aldehyde product mixtures may be separated from the other components of the crude reaction mixtures in which the aldehyde mixtures are produced by any suitable method such as, for example, solvent extraction, crystallization, distillation, vaporization, wiped film evaporation, falling film evaporation, phase separation, filtration, or any combination thereof. It may be desired to remove the aldehyde products from the crude reaction mixture as they are formed through the use of trapping agents as described in WO 88/08835. One method for separating the aldehyde mixtures from the other components of the crude reaction mixtures is by membrane separation, which is described, for example in U.S. Pat. Nos. 5,430,194 and 5,681,473.

As indicated above, desired aldehydes may be recovered from the reaction mixtures. For example, the recovery techniques disclosed in U.S. Pat. Nos. 4,148,830 and 4,247,486 can be used. For instance, in a continuous liquid catalyst recycle process the portion of the liquid reaction mixture (containing aldehyde product, catalyst, etc.), i.e., reaction fluid, removed from the reaction zone can be passed to a separation zone, e.g., vaporizer/separator, wherein the desired aldehyde product can be separated via distillation, in one or more stages, under normal, reduced or elevated pressure, from the liquid reaction fluid, condensed and collected in a product receiver, and further purified if desired. The remaining non-volatilized catalyst containing liquid reaction mixture may then be recycled back to the reactor as may, if desired, any other volatile materials, e.g., unreacted olefin, together with any hydrogen and carbon monoxide dissolved in the liquid reaction after separation thereof from the condensed aldehyde product, e.g., by distillation in any conventional manner.

More particularly, distillation and separation of the desired aldehyde product from the metal-organophosphorous complex catalyst containing reaction fluid may take place at any suitable temperature desired. In general, it is preferred that such distillation take place at relatively low temperatures, such as below 150° C., and more preferably at a temperature in the range of from 50° C. to 140° C. In one embodiment, such aldehyde distillation takes place under reduced pressure, e.g., a total gas pressure that is substantially lower than the total gas pressure employed during hydroformylation when low boiling aldehydes (e.g., C₄ to C₆) are involved or under vacuum when high boiling aldehydes (e.g. C₇ or greater) are involved. For instance, a common practice is to subject the liquid reaction product medium removed from the hydroformylation reactor to a pressure reduction so as to volatilize a substantial portion of the unreacted gases dissolved in the liquid medium that now contains a much lower synthesis gas concentration than is present in the reaction medium to the distillation zone, e.g. vaporizer/separator, wherein the desired aldehyde product is distilled. In general, distillation pressures ranging from vacuum pressures on up to total gas pressure of 340 kPa should be sufficient for most purposes.

In one embodiment, flowing gases may be used in the separation zone to facilitate the aldehyde distillation. Such strip gas vaporizers are described for example in U.S. Pat. No. 8,404,903.

The increased concentrations, high temperatures, and low partial pressures that occur in the separation zone may negatively affect the catalyst, both in terms of catalyst deactivation and/or increased ligand degradation.

Illustrative non-optically active aldehyde products of hydroformylation processes according to embodiments of the present invention will depend on the olefin used as a reactant and can include e.g., propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, 2-methyl 1-butyraldehyde, hexanal, hydroxyhexanal, 2-methyl 1-heptanal, nonanal, 2-methyl-1-octanal, decanal, adipaldehyde, 2-methylglutaraldehyde, 2-methyladipaldehyde, 3-hydroxypropionaldehyde, 6-hydroxyhexanal, alkenals, e.g., 2-, 3- and 4-pentenal, alkyl 5-formylvalerate, 2-methyl-1-nonanal, 2-methyl 1-decanal, 3-propyl-1-undecanal, pentadecanal, 3-propyl-1-hexadecanal, eicosanal, 2-methyl-1-tricosanal, pentacosanal, 2-methyl-1-tetracosanal, nonacosanal, 2-methyl-1-octacosanal, hentriacontanal, and 2-methyl-1-triacontanal, and the like.

In some embodiments where propylene is the olefin that undergoes the hydroformylation reaction, the product is a mixture of n-butyraldehyde and 2-methylpropionaldehyde. As previously noted, the ratio of linear (N) to branched (I) isomers such as the n-butyraldehyde to 2-methylpropionaldehyde (isobutyraldehyde) ratio is conventionally described as the N:I ratio or N:I.

In one embodiment, the catalyst comprises rhodium, triphenylphosphine at a concentration typically utilized in commercial processes (e.g. 10-12 wt. %) and one or more equivalents of tetraphosphine. In such an embodiment, the N:I may be increased by simply adding tetraphosphine without the need for the process fluid to be dumped or removed from the system. This particular embodiment precludes the need for an entirely new catalyst charge and thereby avoids the costs associated with precious metal recovery (PMR), and may be implemented in a short period of time, thus avoiding the need for prolonged shut downs. The resulting catalyst will produce a higher percentage of n-butyraldehyde relative to isobutyraldehyde than the rhodium-TPP catalyst.

In one embodiment, the catalyst composition comprises rhodium, triphenylphosphine at concentrations (e.g., 5-6 weight %) which is lower than typically utilized in commercial processes (e.g., 10 weight % or more), and one or more equivalents of tetraphosphine. For example, a commercial operation wherein the existing rhodium-TPP catalyst solution is aged, but still able to meet production targets, might choose to remove a portion of the catalyst (e.g., 50% of the process fluid) and subsequently add some fresh rhodium and tetraphosphine. Although such an embodiment will involve some PMR expense for the portion of the process fluid removed, the resulting N:I will be higher than the original rhodium-TPP catalyst.

In one embodiment, the catalyst comprises rhodium, triphenylphosphine (e.g. 2-4 wt. %) and one or more equivalents of tetraphosphine. For example, a commercial rhodium-TPP plant wherein the catalyst solution has reached the end of its useful life due to intrinsic deactivation, may choose to dump all of the existing process fluid and charge a fresh catalyst comprised of rhodium, 2-4 wt. % triphenylphosphine and one or more equivalents of tetraphosphine. Such a process would deliver higher selectivity to linear aldehyde than the original rhodium-TPP catalyst. And while the rhodium in the original process fluid would need to recovered, implementing the process of the invention would not require extensive reaction system cleaning or additional process equipment.

In one embodiment, the catalyst comprises rhodium, one or more equivalents of tetraphosphine, and triphenylphosphine (e.g. 1.5-2 wt. %). For example, a process utilizing a catalyst comprised of rhodium and tetraphosphine may choose to add triphenylphosphine to lower the N:I. Although the linear isomer is typically of higher value, commercial operations may choose to make more isoaldehyde due to shifting product demands.

In one embodiment, the catalyst comprises rhodium, one or more equivalents of tetraphosphine, and a monophosphine (e.g. at least 1.5 wt %). For example, a process utilizing a catalyst comprised of rhodium and a monophosphine (i.e. other than TPP) may choose to add tetraphosphine to increase N:I.

In one embodiment, a catalyst solution comprising rhodium, one or more equivalents of tetraphosphine, and a monophosphine is subjected to conditions in the catalyst-product separation zone that preferentially volatilize at least some of the free monophosphine. Stated another way, lowering the concentration of the monophosphine in the reaction fluid via volatilization (e.g., vaporization) will increase the observed N:I. While the tetraphosphines are high molecular weight compounds of exceptionally low volatility, the volatility of monophosphines is known, and the ability to regulate their concentration within a reaction fluid is known to those of ordinary skill in the art. For example, U.S. Pat. No. 5,110,990 describes how to minimize volatilization of monophosphines in a reaction fluid such that one of skill in the art would understand that volatilization of monophosphine in a reaction fluid can be promoted by not implementing the procedures described in that patent.

Some embodiments of the invention will now be described in more detail in the following Examples.

EXAMPLES

All parts and percentages in the following examples are by weight unless otherwise indicated. The concentration of Ligand A is expressed as equivalents, based on moles of Ligand A per mole of rhodium. Pressures in the following examples are given as pounds per square inch gauge unless otherwise indicated. All manipulations such as preparation of catalyst solutions are done under inert atmosphere unless otherwise indicated. Comparative Experiments are not embodiments of the invention.

Gas compositions (mole %) are measured by gas chromatography (GC) and partial pressures are then calculated based on the total pressure using Raoult's law.

Free tetradentate phosphine concentration is measured by High Pressure Liquid Chromatography (HPLC). In order to prevent oxidation during analysis, the phosphines are derivatized to stable phosphine sulfides by mixing with a sulfur-saturated diluent (50:50 by volume acetonitrile:THF saturated with elemental sulfur).

External standard HPLC analyses are performed on an Agilent 1200 Infinity Series HPLC equipped with an UHPLC SB-C8 3.0 mm, 1.8 urn guard column followed by a Zorbax SB-C8 analytical column (3.0×150 mm). Solvent gradient is 55% water with a balance of acetonitrile for 4 minutes; then adjusted to 20:80 water:acetonitrile for 22 minutes, and finally back to the original composition for the remainder of the 35 minute run. Solvent flow rate is 1.00 mL/min throughout, with the column temperature maintained at 40° C. Two microliters of sample is injected into the system; the multi-wavelength UV detector is set at 240 nm.

Preparation of Ligand A

The tetradentate phosphine compound Ligand A is used in these examples and is prepared as set forth below.

Synthesis of 1,1′-biphenyl-2-2′,6,6′-tetracarboxylic Acid

A 5 L jacketed reactor equipped with an overhead stirrer, bottom drain valve and water cooled condenser is charged with 1 L of methylene chloride and 50 g (0.247 mol) of pyrene. The mixture is stirred until the pyrene dissolves, after which 0.25 L of acetonitrile, 1.5 L of deionized water and 2.0 g of ruthenium (III) chloride are added. The resulting biphasic mixture is stirred vigorously and cooled to 18° C. by circulating cooling fluid through the jacket. Sodium periodate is then added in small portions (500 g total; 2.34 mol) over a period of 2.5 hours while maintaining a reactor temperature of 23-27° C. The reaction mixture which is initially brown in color quickly turns dark brown and finally brownish green. After stirring overnight (18 h) agitation is stopped and the layers allowed to separate. The lower layer is drained into a Buchner funnel to collect the crude green/brown solid product which is washed with methylene chloride (2×500 mL) and dried on the filter by flowing air. The solid is then returned to the reactor and refluxed with 1.5 L of acetone for 1 h. After cooling to room temperature, the yellow solution is drained into a Buchner funnel and the filtrate concentrated on a rotary evaporator leaving a yellow solid. The crude tetra acid product is dried in a vacuum oven at 70° C. overnight and used without further purification.

Synthesis of 1,1′-biphenyl-2,2′,6,6′-tetramethanol

The 5 L reactor used in the previous step is dried and purged with nitrogen overnight. Crude 1,1′-biphenyl-2-2′,6,6′-tetracarboxylic acid (50.0 g, 0.152 mol) is charged along with 1.5 L of THF under nitrogen. The resulting solution is stirred and cooled to 0° C. by circulating chilled fluid through the jacket of the reactor. A solution of lithium aluminum hydride in THF (1M; 666 mL; 0.665 mol) is then added via a peristaltic pump over 2 hours. During this time the mixture is stirred vigorously and the reactor temperature is maintained at 0-2° C.; for safety purposes a slow purge of nitrogen is applied to the reactor and the vent stream is passed through a condenser to sweep the reactor of evolved hydrogen. After the lithium aluminum hydride addition is complete, the reactor is stirred cold for an additional 15 minutes, then allowed to warm slowly to room temperature. After stirring at room temperature for 30 minutes, the reactor contents are heated to 65° C. and stirred overnight under a slow nitrogen purge. The next morning the reactor is cooled to 0° C. and quenched with 25 mL of water added slowly via the peristaltic pump, followed by 50 mL of 10% NaOH and 75 mL of water at 0-7° C. over a period of 1.5 hours. The quench procedure evolves hydrogen, and is therefore performed with a nitrogen sweep. The quenched solution is allowed to warm slowly to room temperature and then drained from the reactor into a Buchner funnel. The solids thus collected are washed with hot THF (3×300 mL). The volatiles are removed from the combined filtrate on a rotary evaporator to leave 35 g of a light yellow solid. The solids were dissolved in hot ethanol, filtered, and the solvent removed on a rotary evaporator. Drying overnight in a vacuum oven left 32.3 g of light yellow product (77.1% yield, ca. 97% purity). ¹H NMR (400 MHz, DMSO). δ 7.46 (d, J−6.8 Hz, 4H), 7.39 (dd, J=8.6, 6.4 Hz, 2H), 4.99 (t, J=5.3 Hz, 4H), 3.94 (d, J=5.3 Hz, 8H) ppm. ¹³C NMR (400 MHz, DMSO) δ 139.3, 133.1, 127.3, 125.4, 60.4 ppm.

Synthesis of 2,2′6,6′-tetrakis(chloromethyl)-1,1′-biphenyl

The 5 L reactor is dried and purged with nitrogen overnight and then charged with 1,1′-biphenyl-2,2′,6,6′-tetramethanol (45 g; 0.164 mol), methylene chloride (450 mL) and dimethylformamide (1 mL). The resulting yellow solution is stirred and cooled to 0° C. Thionyl chloride (1,071 g, 9.01 mol) is then added slowly via peristaltic pump over a 2 hour period, keeping the reactor temperature near 0° C.; during the addition the reactor is swept with nitrogen to remove the HCl and SO₂ which are generated, with the off gases passed through a water scrubber. The reaction solution is then allowed to warm to room temperature and stir for 30 minutes before heating to reflux (ca. 45° C.) overnight. The next day, the solution was cooled to 15° C. and discharged from the reactor. The methylene chloride was removed by distillation at atmospheric pressure, and the residual thionyl chloride removed by vacuum distillation. The resulting residue was dried first on a rotary evaporator followed by drying in a vacuum oven at 60° C. overnight to leave 58.1 g of yellow solid. (100% yield, ca. 95% purity). ¹H NMR (400 MHz CDCl2) δ 7.66-7.60 (m, 4H), 7.56 (dd, J=8.8, 6.4 Hz, 2H), 4.28 (s, 8H) ppm. ¹³C NMR (400 MHz, CDCl2) δ 136.9, 135.5, 131.3, 130.3, 45.0 ppm.

Synthesis of (biphenyl-2,2′,6,6′-tetramethanediyl)tetrakis(diphenylphosphane) (Ligand A)

Lithium wire (2.1 g, 300 mmol) is cut into small pieces and charged into a 250 mL flask in a dry box along with anhydrous THF (130 mL). The suspended solution is transferred to a Schlenk line and chilled in an ice water bath under nitrogen. Chlorodiphenylphosphine (28.1 mL, 151.7 mmol) was added dropwise at 0° C. over a period of 50 minutes and then stirred an additional 30 minutes at 0° C. During this time the color changes from cloudy yellow to red. The solution was transferred to a dry box and stirred at room temperature overnight. The next morning the solution was cannula filtered into a clean, dry 500 mL round bottom flask, transferred to the Schlenk line and chilled to −78° C. A solution of 2,2′6,6′-tetrakis(chloromethyl)-1,1′-biphenyl (12.7 g, 37 mmol) in THF (60 mL) was added dropwise over 50 minutes, and then stirred cold for an additional 20 minutes. The solution is then allowed to warm slowly to room temperature, and then transferred to the dry box and stirred overnight. Degassed methylene chloride (300 mL) and water (150 mL) were then added, and the resulting mixture allowed to separate. The lower layer was transferred to a round bottom flask and concentrated on a rotary evaporator at 30° C. to leave a solution of crude product in THF. While heating this solution at 65° C. under flowing nitrogen, degassed ethanol (100 mL) is added slowly. White solid began precipitating during the ethanol addition. The mixture was then allowed to cool and placed in a refrigerator overnight; the resulting solids are collected the next day by filtering in the dry box, and washing with ethanol (2×50 mL). Drying under vacuum overnight leaves the desired product as a white powder (90% yield, 99% purity). ³¹P NMR (400 MHz, CDCl3) δ −14.5 ppm. ¹H NMR (400 MHz, CDCl3) δ 7.30-7.17 (m, 40H), 6.91-6.82 (m, 2H), 6.72 (d, J=7.7 Hz, 4H), 3.21 (s, 8H) ppm. Ligand A, the tetradentate phosphine, has the following structure:

Comparative Ligand B

Comparative Ligand B is BISBI (neither a monophosphine nor a tetradentate phosphine) which is known to produce an active and selective hydroformylation catalyst. Methods of preparation for BISBI and examples of its use as a hydroformylation ligand may be found for example in U.S. Pat. No. 4,694,109. The BISBI used in the Comparative Experiments below was purchased from Proactive Molecular Research of Alachua, Fla. and used as received. The structure of BISBI (Ligand B) is shown in FIG. 2.

General Procedure

Unless otherwise indicated, examples and comparative experiments are conducted in 90 mL flow-through Fisher Porter reactors equipped with means for accurate control of temperatures and gas flows. Reactor off gases are analyzed by online GC to determine partial pressures. Mixing in the flow-through reactor is effected by continuous gas flow via a sparger at the bottom of the reactor. This reactor design is described in detail in U.S. Pat. No. 5,731,472, the teachings of which are incorporated by reference.

Reaction rates are expressed as moles of aldehyde produced per volume of catalyst solution per unit time (moles/L-hour); this value is additionally divided by the propylene partial pressure to help dampen the effects of small, unavoidable fluctuations in the propylene feed rate (rate/olefin). Product selectivity is expressed as the ratio of linear (normal) aldehyde versus branched (iso) aldehyde (N:I).

Example 1

A reactor is charged with tetraglyme (20 mL), rhodium (300 ppm), and triphenylphosphine (TPP) (12 wt. %). Hydroformylation is established under 10 psi CO, 50 psi H₂ and 20 psi propylene at 90° C. Baseline reaction rate and N:I are measured. After running overnight, Ligand A (4 equivalents) is added and the impact on performance is determined.

The results for Example 1 are shown in Table 1.

TABLE 1 Following addition Initial of Ligand A Example rate/olefin N:I rate/olefin N:I 1 0.0560 9.6 0.0224 29.0 The results of Table 1 show the ability to increase the N:I of a process comprising rhodium and TPP, wherein the TPP is present at the concentrations typical for commercial operations, by simply adding Ligand A.

Examples 2-5

Each of four reactors is charged with tetraglyme (20 mL), rhodium (200 ppm), Ligand A (1.5 or 5 equivalents relative to rhodium), and TPP (5 or 10 wt. %). Hydroformylation is established under 20 psi CO, 50 psi H₂ and 20 psi propylene at 90° C. The hydroformylation rates and N:I are measured.

The results of Examples 2-5 are shown in Table 2.

TABLE 2 TPP Ligand A Example wt % (equiv) Rate/olefin N:I 2 5 1.5 0.0308 19.3 3 5 5.0 0.0278 27.7 4 10 1.5 0.0215 14.3 5 10 5.0 0.0167 23.2 The results of Table 2 show the ability to vary the N:I ratio by adjusting ligand concentrations. Specifically, increasing the concentration of Ligand A results in a higher N:I (e.g., Example 2 vs. Example 3); conversely, increasing the TPP concentration lowers the N:I (e.g. Example 2 vs. Example 4, and Example 3 vs. Example 5). This also shows that the N/I can be increased from around 19 (Example 2) to around 28 by the addition of Ligand A (Example 3), but then reduced again to around 23 by addition of TPP (Example 5); thus the initial change is reversible.

Examples 6-10

Each of six reactors is charged with tetraglyme (20 mL), rhodium (200 ppm) Ligand A (1.5 equivalents relative to rhodium), and varying amounts of TPP. Hydroformylation is established under 20 psi CO, 50 psi H₂ and 20 psi propylene at 90° C. The results for Examples 6-10 are shown in Table 3.

TABLE 3 TPP Example wt % Rate/olefin N:I 6 8 0.0183 15.2 7 6 0.0214 17.7 8 4 0.0275 20.5 9 2 0.0427 27.2 10 1 0.0570 31.1 The dependence of N:I on TPP concentration is clearly demonstrated.

Comparative Experiments A-D

The procedure of Examples 2-5 is repeated, with the exception of the use of Comparative Ligand B. Because Comparative Ligand B has two phosphorous moieties per molecule compared to four phosphorous moieties per molecule of Ligand A, twice the amount of Ligand B is employed. The results for Comparative Experiments A-D are summarized in Table 4.

TABLE 4 Comparative TPP Com. Lig B Experiment wt % (equiv) Rate N:I A 5 3.0 0.0243 7.6 B 5 10.0 0.0143 13.0 C 10 3.0 0.0167 7.8 D 10 10.0 0.0114 10.5 The catalysts comprising rhodium, TPP, and Comparative Ligand B demonstrate a generally lower hydroformylation rate and do not produce an N:I in excess of 13 under the test conditions. Without being bound by theory, the relatively low reaction rate and N:I suggest that the rhodium-BISBI catalyst is more readily inhibited by TPP, and thus the resulting mixture of active complexes contains a lesser amount of the active and selective rhodium-BISBI complex.

In contrast, the catalysts comprising rhodium, TPP and Ligand A under the same conditions demonstrates a faster rate as well as an N:I ranging from 14 to about 28 (see Table 2). Selectivity to the linear aldehyde may thereby be increased by more than 3% using a process according to some embodiments of the invention, which could provide substantial financial benefit in a commercial operation. 

What is claimed is:
 1. A method of controlling a hydroformylation process for producing aldehydes, the process comprising contacting an olefin with carbon monoxide, hydrogen and a catalyst, the catalyst comprising (A) a transition metal, (B) a monophosphine, and (C) a tetraphosphine having the following structure:

wherein each P is a phosphorous atom, and each of R¹-R⁴⁶ are independently hydrogen, a C1 to C8 alkyl group, an aryl group, an alkaryl group, or a halogen, the contacting conducted in one or more reaction zones and at hydroformylation conditions to produce a blend of normal (N) and iso (I) aldehydes at a N:I ratio, the method comprising at least one of: (1) increasing the N:I ratio by adding additional tetraphosphine to a reaction zone; (2) decreasing the N:I ratio by adding additional monophosphine to a reaction zone; or (3) increasing the N:I ratio by volatilization of the free monophosphine.
 2. The method of claim 1, wherein the monophosphine is triphenylphosphine.
 3. The method of claim 1, wherein the transition metal comprises rhodium.
 4. The method of claim 1, wherein each R¹-R⁴⁶ are hydrogen.
 5. The method of claim 1, wherein the olefin is propylene.
 6. The method of claim 1, wherein the amount of monophosphine in the reaction zone is greater than or equal to 1.5 weight percent based on the total weight of reaction fluid in the reaction zone.
 7. The method of claim 1, wherein the amount of monophosphine in the reaction zone is from 1.5 to 13 weight percent based on the total weight of reaction fluid in the reaction zone.
 8. The method of claim 1, wherein the amount of tetraphosphine in the reaction zone is greater than or equal to 0.06 weight percent based on the total weight of reaction fluid in the reaction zone.
 9. The method of claim 1, wherein the amount of tetraphosphine in the reaction zone is from 0.1 to 9 weight percent based on the total weight of reaction fluid in the reaction zone. 